Well, as soon as SPRING FINALLY GETS HERE the tops on convertible cars will be going down. Convertible (reversible) dresses, however, are best sewn from the bottoms up (IMHO-hem first).
When knitting sweaters - top down is good. The more complex parts are done while you are still excited about a new project, the cast on edge gives good elasticity at the neck edge, and the "mindless" knitting is done toward the end.
HOWEVER! Never vacuum stairs top down or THIS COULD HAPPEN: terrifying episode where said lightweight upright suddenly lunges toward you while swirling dust and cat fur, growling ferociously, (never purchase a vaccum whose handle looks very much like a blunt WEAPON) - incurring blunt force trauma.
Bottoms UP to Top downers!